Bevel wheel



Junev23, 1931. GL VEBER 1,811,446

` BEVEL WHEEL Filed sept.' 26.1927 4 sheets-Sheen 1 7.21 M912 for G.VEBER June 23, 1931.

BEVEL WHEEL Filed Sept. 26. 1927 4 Sheets-Sheet 2 ozzzefyy June l23,1931. G. VEBER 1,811,446

BEVEL WHEEL Filed Sept. 26, 1927 4 Sheets-Sheet 3 Zzz 06,12 for June 23,1931. G. VEBER 1,811,446

BEVEL WHEEL l Filed Sept. 26. 1927 4 Sheets-Sheet 4 E910. Egli PatentedJune 23, 1931 UNITED STATES PATENT OFFICE GEORGES VEBER, OF EPINAL,FRANCE, ASSIGNOR TO ROGER GABRIEL LOUIS COUTANT,

OF VINCENNES, SEINE, FRANCE BEV'ELy WHEEL i Application filed September26, 1927, Serial No. 222,060, and in France November 5, 1926.

The invention has for object bevel wheels, the teeth of which are suchthat they can be cut by means of a milling cutter having a uniformprofile, the gearing Contact remaining however correct.

According to the invention, the profiles of the tooth to be cut, at thevarious points of its length, are constituted by arcs sensiblysuperposable of one and the same involute; the angle of pressure, of oneof the ends to the other of the teeth, varying accordingly.

The edges of the teeth are not convergent, butthe gearing contactremains correct, if the same variation of the angle of pressure existsin the two associated wheels. A bevel wheel can, in fact, be consideredas formed by the assemblage of an infinity of bevel or conical discs, ofdecreasing diameters, fitted in each other, and toothed. on their edges.It suffices that the teeth of each of these elementary discs can gearwith those of the correspond` ing disc on the associated wheel, in orderthat the engagement of the wheels should be satisfactory.

The accompanying drawings illustrate by way of example, one of the formsof con'- struction of the bevel wheel.

Fig. l shows how varies the profile along a tooth cut in the ordinarymanner.

Fig. 2 is an axial diagrammatic section of a pair of bevel wheels.

Figs. 3, 4 and 5 are plans showing'how are traced the teeth of thewheels in accordance with the invention.

Fig. 6 shows that the profile of the said teeth remains practicallyidentical throughout their length.

Fig. 7 is a section, through an axial plane, of the milling cutter. v

Fig. 8 is a front view of the milling cutter.

Fig. 9 is a side view of the same.

Fig. 10 shows the intersection points of the pitch line with the outlineof the cutter.

Fig. 11 shows the desirable profile.

Fig. 12 is a diagrammatic plan view of a machine. Y c In 'anordinaryfbevel wheel, in which the flanks vor'sides of the teethconverge(Fig. l), all the sections made transversely to the teeth give similarsections, the dimensions of which go on decreasing. The two curved edgesof these sections are always two arcs of involute. The radius of thedeveloped circle which has generated them varies proportionally to theradius of the pitch circle of the teeth at the section underconsideration, and the pressure angle (14o 30') remains the same allalong the tooth.

It will be understood that such a flank, formed by a succession ofsimilar curves, but of different dimensions, cannot be cut by a singlemilling cutter. v Fig. l, which represents three sections made in atooth with a constant pressure angle, shows the impossibility ofeffecting such a cutting.

According to the present invention, the pressure angle does not remainconstant, but varies in a continuous manner along the tooth. Theprofiles of the successive sections are no longer similar to each other,but approximately superposable. Such a form of teeth preserves a propergearing engagement whilst greatly simplifying the cutting.

The gearing engagement of the teeth thus obtained is theoreticallyperfect. In fact, a conical gearing can be considered as formed by theassemblage of an infinity of conical discs of decreasing diameters,fitted into each other and toothedv on their edge (Fig. 2).

It suffices that the teeth of each elementary disc 25,' 26, 27 should becapable of gearing with those of the corresponding disc of theassociated wheel 25', 26', 27 in order that the gearing engagement ofthe wheels should be satisfactory. This result is obtained if theprogressive variation of the pressure angle is the same for the twowheels in contact.

The great simplification of the cutting arises from the fact that teethhaving a variable pressure angle can be cut by means of a milling cutterhaving a uniform profile.

In fact, supposing we have (Figs. 3, 4, 5) three sections made in abevel gear tooth, at both ends and in the middle. The radii R, R', R ofthe pitch circles 28, 29, 30 diminish in the same proportion as theradii of the top and bottom circles of the teethy It different values`are given to the pressure angles; a-aa, the radii of the circles to bede-k veloped 7', 7", r will no longer be in one and the same ratio R,R', R, the involutes d, d', d obtained with lthe circles of radius1341', r will no longer be similar. If these three involutesy aresuperposed (Fig. 6) by causing to coincide the origins of the threeinvolutes (points where they leave the foot or base circle of theteeth), it will be seen that for pressure angles 0;, a', c suitablygraduated (here: 22-21-20), a nearly absolute coincidence is obtained,of the order of a hundredth ofV a millimeter, on a length equal orsuperior to the height of the tooth.

The iirst involute a corresponds to the large f diametral pitch of thetooth; it mingles with the second involute a (corresponding Ito the meandiametral pitch) on a length kfw-fn, height of the tooth at this place,and with the third involute a (correspondingto the small diametralpitch) throughout the height of the tooth at the small diametral pitch.

The involute a may therefore be considered as giving the very exactprofile of the tooth throughout its length, by admitting that thepressure angle has constantly varied. p In practice, this angle variesfrom 18o to 25, according to the relative length of the tooth. As theassociated wheel is cut by the same method, at each point of contact ofthe wheels, are two involutes traced with the same pressure angle andthe running is perfeet.

For cutting a bevel wheel according to the invention, use can be made ofa milling cutter toothed only on an angle A (Figs. 3 and 9) and havingits teeth arranged on a helix shaft having a pitch p.

The flanks of the milling cutter have for profile an involute (Fig. 7),traced with a pressure angle of 22o in the above example.

The blank to be cut continuously rotates with a speed V; the millingcutter rotates at the speed 'V such that: V=n fv, ri-being the number ofteeth of the wheel to be cut.

The teeth of the milling cutter enter-"more and more intothe blank inproportion as'the feed-proceeds. The thickness of a tooth of themilling'cutter (Fig. 77) atthelevel of the-pitch circles, at the small,`mean and large diametral pitches is respectively, e-c-e.` The teeth ofthe milling rcutter Cut hollows having a. length Z-Z-Z, on these variouspitch circles.V f f These widths are equal to those of the teeth at thelevel of the pitchcir'cle under consideration, to which is added thecircular displacement kof the gear during the passage-of Y Sametime,owing to their arrangement on an larc of a hel-ix.V

' One Ahas therefore, for Vthe .eXtreme sec.-

tions of the set of teeth, the two following equations:

eifv.A-p.A=1 (l) ell+lvll Alep. Ll/:l/

in which: 6 6 are the widths of the teeth of the milling cutter at thelevel of the two pitch circles under consideration. '0, A', o, A are thecircular displacements of the gear during the cutting of a tooth,thesedisplacements are equal to the pitch circumference multiplied by Aand divided by 360. p. A represents the side displacement of the teethof the milling cutter Vduring cutting; it is equal to p. the pitch ofthe' milling cutter, multiplied by A and divided by 360.- ll and l arethe widths which must have the teeth formed on the two pitch circlesunder consideration.

By solving these two equations, one iinds p the pitch of the cutter andA the toothed angle of the cutter. y

t the middle of the length of theftooth, the width e of the cutter atthe level of the corresponding pitch circle, the circular displacemento', A of the blank during cutting, the pitch p of the cutter,`itstoothed angle and the width of the hollow 'formed at this point, areconnected by the equation: ci-o. A-p. A=l (Fig. 3)

If one in serts in this equation the values of p and of A taken from theEquations' l and 2, these values verify theEquation 3 with a very greatapproximation, more than sufiicient in the practice. n

For instance, for a cutter cutting a wheel having 42 teeth,with amaximum diametral pitch of 3, at the diametral pitches 3 and 2, 5 and 2,the following values are obtained for e: 3,10 millimeters, 3,63millimeters, 4.14 millimeters, this with.l the relative displacements,corresponds to cutting widths of 3,14 millimeters, 3,92 millimeters,3,71 millimeters. The angle `A is of 60, the pitch pcf 6 millimeters. v

rlhe widths e are moreover to berectiiied, as, during cutting,thecutter, the axis of which'remains in factixed, seemsto rock from rightto left relatively to the' teeth ywhich effect a rotation. 'Thiseffectis cor' rected by causingV the profile of the vmilling cutter to pivotabout the suitable point, according to an angle equal to n being thenumber of teeth of thejwheel to be cut. This pivoting' renders theprofile thinner in lthe upperpart and widens it at thebase.

Fig. 10 shows, at 31, 32, 33, the intersection points of the pitch linewith the koutline of the milling cutter, for -the little Vaverage y andlargeA diametral pitch, respectively..

fll

For obtaining rigorously accurate toothed wheel it is necessary to havethe three points 31', 32, 33 on a same straight line, whereas, they are,at the contrary, situated on an evolvent are. v

According to the invention, the accurate cutting is obtained bydisplacing the milling cutter and the wheel to be cut, one relatively tothe other, during the cutting operation, not only in a single direction,but also according to two directions at right angles, so that the points3l, 32, 33, are on the same straight line (Fig. 11).

Use can be made, e. g. of the device shown at the Fig. l2 in which themilling cutter is v shown at 34, the wheel to be cut at 35, 36 being theframe. The latter is connected, by means of an arm 37, to an eccentric38 on which oscillates the said arm, the initial position of theeccentric being adjustable at will. The eccentric 38 is connected bymeans of the crank lever 39 and the rod 40 to a iXed point 4l. It can beseen that, during the displacement of the frame, in the direction of thearrow 42, the eccentric rotates and displaces'also the frame in thedirection 43 (or in a reverse direction), so permitting to obtain thedesired result.

The teeth, in accordance with this invention, can also be cut onordinary machines, with a cutter having a suitable profile. The movementof this cutter along generating lines of the cone to be provided withteeth is then accompanied only by a simple rotation of the blank,instead of the usual complex displacements.

It is to be mentioned that all means for cutting bevel wheels in such amanner that the proile of the teeth, at various points, is constitutedby superposable arcs of involute, with variable pressure angles can beemployed; in particular, use can be made of milling cutters whichinstead of having only 4 or 5 teeth and a smooth portion, have one ortwo turns of teeth, among which four or five have anormal thickness andexecute the finishing of the profile; the others on either side of thefirst ones, become thinner and thinner and serve to dig up the blank. Ingeneral, the method of cutting can be of any type.

What l claim as my invention and desire to secure by Letters Patent is Abevel gear wheel, wherein the addendum cone and the dedendum cone havethe same vertex and wherein the teeth are straight and symmetrical andhave a section in the form of an involute, which remains the same theentire length of the tooth, so that the pressure angle varies from oneend of the tooth to the other.

In testimony whereof I have signed my name to this specification.

GEORGES VEBER.

